Study on Three-Dimensional Nonlinear Viscoplastic Model Based on Creep Characteristics of Sandstone

Abstract

In order to describe the creep behavior of rock, triaxial compression creep tests of sandstone under
different confining pressures were carried out. The results show that the steady creep stage is a process of
developing and expanding microcracks in rock, and the steady creep rate and confining pressure increase by
power function. The long-term strength of sandstone under confining pressure of 5MPa, 10MPa and 15MPa
is 19.8 MPa, 22.3 MPa and 24.7 MPa, respectively. The long-term strength increases with the increase of
confining pressure. Based on the nonlinear characteristics of rock creep, a viscoelastic modulus E(p)
associated with confining pressure is defined. A E(p,t) that can reflect the influence of rock creep by time
and confining pressure is obtained by derivation transformation, which is applied to the improved Burgers
model to obtain a new one-dimensional creep constitutive model. It can be extended to three-dimensional
stress state to obtain a new three-dimensional nonlinear mechanical model, and the identified creep test data,
prediction results comparison and analysis prove the feasibility and rationality of the model. The research
results provide some reference for the simulation of creep behavior of rock under three-dimensional stress
state.